Chromosomal differentiation in Helianthus annuus var. macrocarpus: heterochromatin characterization and rDNA location

Abstract

The 2n = 34 chromosomes of the inbred line HA89, and the Flamme and Mirasol hybrids of Helianthus annuus var. macrocarpus possess centromeric heterochromatin as established by Giemsa C-banding. This heterochromatin can not be differentiated by fluorochromes such as DAPI or Chromomycin A3, with selective affinity for specific DNA base pairs. This situation probably results from either a balanced AT/GC composition of the involved repeat or the existence of alternating repetitive sequences of opposite base pair composition in these heterochromatic areas. However, there is also heterochromatin associated with the secondary constrictions on three pairs of chromosomes. This heterochromatin appears to be GC-rich according to its response to the fluorochrome treatments, thus indicating heterochromatin heterogeneity in H. annuus. Silver staining reveals the existence of active NORs associated with these secondary constrictions. In situ hybridization with an rDNA probe confirms these results and makes the existence of other inactive rDNA sites unlikely. These results are relevant to evolutionary and breeding studies on sunflowers.

Heterochromatin differentiation in holocentric chromosomes of Rhynchospora (Cyperaceae)

“…The first type, characterized by CMA 3 + /DAPI 0 in R. ciliata, coincided with those obtained by Giemsa banding and was similar to that found in Drosera puchella and D. scorpioides holocentric chroa b c mosomes (Sheikh and Kondo, 1996). These regions could correspond to heterogeneous heterochromatin sites, where GC-rich segments are intercalated with AT-rich ones, as described by Guerra (1989) and Cuellar et al (1996). The second type, CMA 3 + /DAPI -bands present in most of the species, and the third type, CMA 3 -/DAPI + blocks, found only in R. globosa, seem to correspond to GC-rich and AT-rich DNA sequences, respectively (Schweizer, 1976).…”

Patterns of heterochromatin distribution in plant chromosomes

“…In addition, non-fluorescent DNA-ligands, like dystamycin A, may also be used to intensify the CMA or DAPI staining (Schweizer, 1983;Fuchs et al, 1998). However, not all AT-rich or GC-rich HC reacts equally to these fluorochromes (see e.g., Schwarzacher and Schweizer, 1982;Kenton, 1991;Bennett et al, 1995) and some C-banded positive regions react neutrally with fluorochromes, i.e., they fluoresce with the same brightness as euchromatin (Morawetz, 1986a,b;Röser, 1994;Galasso et al, 1996b;Cuellar et al, 1996). Other C-bands, fluoresce with the same intensity when stained with fluorochromes with different base-specificities, such as CMA and DAPI (Loidl, 1983;Guerra, 1989;Okada, 1991;Berg and Greilhuber, 1993).…”

“…In some cases, besides CMA and DAPI, other fluorochromes were also used as primary stains (Hoshi et al, 1995;Sato and Yoshioka, 1984) or as counterstains (Deumling and Greilhuber, 1982;Jamilena et al, 1990;Cuellar et al, 1996). Quinacrine was the third most frequently used fluorochrome (10 species), followed by Hoechst 33258.…”

Intraspecific polymorphism of ribosomal DNA loci number and morphology in Brachypodium pinnatum and Brachypodium sylvaticum

“…2K -2L; yellow arrows). The correlation between CMA+ bands and 35S rDNA sequences in plants is well known and was reported for species such as Helianthus annuus [53]. In species that form the 'U triangle' within the Brassica genus, the number of CMA+ bands was shown to correspond to the number of 35S rDNA loci, irrespectively of their size [54].…”